Remotely powered electronic devices and related systems are known. For example, U.S. Pat. No. 5,099,227, issued to Geiszler et al. and entitled “Proximity Detecting Apparatus,” discloses a remotely powered device which uses electromagnetic coupling to derive power from a remote source, then uses both electromagnetic and electrostatic coupling to transmit stored data to a receiver, often collocated with the remote source. Such remotely powered communication devices are commonly known as radio frequency identification (“RFID”) tags.
RFID tags and associated systems have numerous uses. For example, RFID tags are frequently used for personal identification in automated gate sentry applications, protecting secured buildings or areas. These tags often take the form of access control cards. Information stored on the RFID tag identifies the tag holder seeking access to the secured building or area. Older automated gate sentry applications generally require the person accessing the building to insert or swipe their identification card or tag into or through a reader for the system to read the information from the card or tag. Newer RFID tag systems allow the tag to be read at a short distance using radio frequency data transmission technology, thereby eliminating the need to insert or swipe an identification tag into or through a reader. Most typically, the user simply holds or places the tag near a base station, which is coupled to a security system securing the building or area. The base station transmits an excitation signal to the tag that powers circuitry contained on the tag. The circuitry, in response to the excitation signal, communicates stored information from the tag to the base station, which receives and decodes the information. The information is then processed by the security system to determine if access is appropriate. Also, RFID tags may be written (e.g., programmed and/or deactivated) remotely by an excitation signal, appropriately modulated in a predetermined manner.
Some conventional RFID tags and systems use primarily electromagnetic coupling to remotely power the remote device and couple the remote device with an exciter system and a receiver system. The exciter system generates an electromagnetic excitation signal that powers up the device and causes the device to transmit a signal which may include stored information. The receiver receives the signal produced by the remote device.
These conventional RFID tags are manufactured such that the integrated circuitry is manufactured separately from the antenna and/or inductor, and the two components are then physically and electrically connected. These components are manufactured separately, in part, due to the cost of manufacturing silicon wafers. It would be cost prohibitive to manufacture both components on a silicon wafer. The antenna and/or inductor is a simple structure and can be manufactured on a less expensive substrate using less expensive processing methods and joined to the integrated circuitry in a later manufacturing step.
Referring to FIG. 1A, conventional RFID tags are formed by a process that includes dicing a wafer manufactured by conventional wafer-based processes into a plurality of die. A die is then placed onto an antenna or inductor carrier (which may contain an antenna, inductor coil or other conducting feature) in a chip-to-antenna attach process. Alternately, the die can be attached to an intermediate carrier (or interposer) in a two-step chip-to-strap/strap-to-antenna attach process.
In the two-step process, a die 120 is attached to an interposer (or carrier) 140. Electrical paths 130 and 132 from the die 120 to relatively larger and/or more widely distributed areas (e.g., 134 or 136) for attaching ends of the antenna are present in certain locations on the interposer 140. This assembly may then be attached, as shown in FIG. 1B to a support film 150 containing inductor/antenna 152. Because the pads 134 and 136 (together with the paths 130 and 132 and the die 120) connect the ends of the antenna 152, the assembly on the interposer 140 is sometimes known as a “strap.” This attach process may include various physical bonding techniques, such as gluing, as well as establishing electrical interconnection(s) via wire bonding, anisotropic conductive epoxy bonding, ultrasonics, bump-bonding or flip-chip approaches. Also, the attach process often involves the use of heat, time, and/or UV exposure. Since the die 120 is usually made as small as possible (<1 mm2) to reduce the cost per die, the pad elements for external electrical connections to the die 120 may be relatively small. This means that the placing operation should be of relatively high accuracy for high speed mechanical operation (e.g., placement to within 50 microns of a predetermined position is often required).
As a whole, the process of picking out a separated (sawn) die, moving it to the right place on the antenna(e), inductor, carrier, or interposer to which it is to be bonded, accurately placing it in its appropriate location, and making the physical and electrical interconnections can be a relatively slow and expensive process. In the case of processes that use an intermediate interposer, cost and throughput advantages are achieved by first attaching the die to a roll of interposer carriers, which can be done quickly and sometimes in parallel, as they are generally closely spaced and other novel placement operations such as fluidic self-assembly or pin bed attachment processes can be done more easily. The carriers generally contain electrical paths from the die to relatively larger and/or more widely distributed areas in other locations on the carrier to allow high-throughput, low resolution attachment operations such as crimping or conductive adhesive attach (somewhat functionally similar to a conventional strap, as compared to a pick-and-place and/or wire bonding based process for direct integration of a chip die to an inductor substrate). In some cases, low resolution attach processes suitable for straps could be performed at costs near $0.003 or less, based on commercially available equipment and materials (e.g., a Mühlbauer TMA 6000 or similar apparatus).
The carriers are then attached to an inductor/antenna 152 such that electrical connections are formed at such other locations. This carrier-based process may also have advantages for flip-chip or bump bonding approaches, where it may be more expensive or disadvantageous to implement the required stubs, bumps or other interconnect elements onto the larger inductor/carrier substrate 150 by conventional means (e.g., wire bonding).
Conventional RFID manufacturing processes, as described above, require the use of either a highly-complex chip-to-antenna attach process or a two-step chip-to-strap/strap-to-antenna attach process. Either process requires high-precision pick-and-place equipment for the chip attach. The high precision pick-and-place equipment has a relatively high capital cost and is typically slower than lower precision equipment. As a result, the conventional attach process has a proportionately high cost relative to the overall manufacturing cost.
The price of tags is a significant focus within the RFID industry. High RFID tag prices have been an obstacle against widespread adoption of RFID technology, especially in item-level retail applications and other low-cost, high-volume applications. One way of reducing tag costs is to develop a tag structure and process that incorporates (and preferably integrates) a less expensive substrate, a stable and effective antenna, RF front end devices, and high resolution patterned logic circuitry.